I must stress before I start that I'm talking about my polytunnel, as Flo would quickly point out it's far too early to sow seed outdoors.
But, I checked the soil temperature in the tunnel today and it's a very nice 10 C about 2" down.
Coupled with my now extensive garden diaries I can see that I sow the same seeds at roughly the same time every year, and this year will be no different.
So today I sowed a pinch of cauliflower and calabrese in pots and started up the heated propagator, also sowed a pinch of Winter Gem lettuce, and in the tunnel I sowed a row of Deuce Provence peas.

Unless we have really, really bad winter (a la 1963) then I should have broccoli heads for cutting about the first week of April, cauliflowers from early May (although I should have some over-wintering ones before that) and peas in mid-May.
As well as lettuces and spring cabbage in March from the greenhouse hydro.

Flo won't even be testing the soil on her allotment in the proper gardener's fashion (bare bum to soil) at present as it's about frozen at the moment.

Couple of weeks back the local vegetable growing cooperative recorded -4.5 degrees c in the poly tunnel that had the paraffin heater on a low setting in it. The grower there was not amused. And yes he does have over wintering stuff in his poly tunnels!

I'm afraid my hungry gap efforts mainly run to sprouting seeds on my windowsill for salads. The temperatures aren't bad here but the light levels are. However that might alter if this hydroponic malarkey takes off (although I don't think we'll be able to sustain ourselves for long with one, 3 pod, unit)!

Maggie

Never doubt that you can change history. You already have. Marge Piercy

I'm surprised you haven't experimented with grow lights, like this for instance. 2 watts for 12 hours a day for a spot plant or seedlings wouldn't cost too much.
I have a strip light version over my windowsill type propagator and it works wonders for non-leggy seedlings.
Just a thought.